<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>svfilter</title>
    <link rel="stylesheet" type="text/css" href="csound.css" />
    <meta name="generator" content="DocBook XSL Stylesheets V1.78.1" />
    <link rel="home" href="index.html" title="The Canonical Csound Reference Manual" />
    <link rel="up" href="OpcodesTop.html" title="Orchestra Opcodes and Operators" />
    <link rel="prev" href="sumarray.html" title="sumarray" />
    <link rel="next" href="syncgrain.html" title="syncgrain" />
  </head>
  <body>
    <div class="navheader">
      <table width="100%" summary="Navigation header">
        <tr>
          <th colspan="3" align="center">svfilter</th>
        </tr>
        <tr>
          <td width="20%" align="left"><a accesskey="p" href="sumarray.html">Prev</a> </td>
          <th width="60%" align="center">Orchestra Opcodes and Operators</th>
          <td width="20%" align="right"> <a accesskey="n" href="syncgrain.html">Next</a></td>
        </tr>
      </table>
      <hr />
    </div>
    <div class="refentry">
      <a id="svfilter"></a>
      <div class="titlepage"></div>
      <a id="IndexSvfilter" class="indexterm"></a>
      <div class="refnamediv">
        <h2>
          <span class="refentrytitle">svfilter</span>
        </h2>
        <p>svfilter — 
      A resonant second order filter, with simultaneous lowpass, highpass and bandpass outputs.
          </p>
      </div>
      <div class="refsect1">
        <a id="idp154402928"></a>
        <h2>Description</h2>
        <p>
      Implementation of a resonant second order filter, with simultaneous lowpass, highpass and bandpass outputs.
    </p>
      </div>
      <div class="refsect1">
        <a id="idp154468992"></a>
        <h2>Syntax</h2>
        <pre class="synopsis">alow, ahigh, aband <span class="command"><strong>svfilter</strong></span>  asig, kcf, kq [, iscl]</pre>
      </div>
      <div class="refsect1">
        <a id="idp154471056"></a>
        <h2>Initialization</h2>
        <p>
      <span class="emphasis"><em>iscl</em></span> -- coded scaling factor, similar to that in <a class="link" href="reson.html" title="reson"><em class="citetitle">reson</em></a>. A non-zero value signifies a peak response factor of 1, i.e. all frequencies other than <span class="emphasis"><em>kcf</em></span> are attenuated in accordance with the (normalized) response curve. A zero value signifies no scaling of the signal, leaving that to some later adjustment (see <a class="link" href="balance.html" title="balance"><em class="citetitle">balance</em></a>). The default value is 0.
    </p>
      </div>
      <div class="refsect1">
        <a id="idp154475360"></a>
        <h2>Performance</h2>
        <p>
      <span class="emphasis"><em>svfilter</em></span> is a second order state-variable filter, with k-rate controls for cutoff frequency and Q.  As Q is increased, a resonant peak forms around the cutoff frequency. <span class="emphasis"><em>svfilter</em></span> has simultaneous lowpass, highpass, and bandpass filter outputs; by mixing the outputs together, a variety of frequency responses can be generated. The state-variable filter, or "multimode" filter was a common feature in early analog synthesizers, due to the wide variety of sounds available from the interaction between cutoff, resonance, and output mix ratios. <span class="emphasis"><em>svfilter</em></span> is well suited to the emulation of "analog" sounds, as well as other applications where resonant filters are called for.
    </p>
        <p>
      <span class="emphasis"><em>asig</em></span> -- Input signal to be filtered.
    </p>
        <p>
      <span class="emphasis"><em>kcf</em></span> -- Cutoff or resonant frequency of the filter, measured in Hz.
    </p>
        <p>
      <span class="emphasis"><em>kq</em></span> -- Q of the filter, which is defined (for bandpass filters) as bandwidth/cutoff. <span class="emphasis"><em>kq</em></span> should be in a range between 1 and 500. As <span class="emphasis"><em>kq</em></span> is increased, the resonance of the filter increases, which corresponds to an increase in the magnitude and "sharpness" of the resonant peak. When using <span class="emphasis"><em>svfilter</em></span> without any scaling of the signal (where <span class="emphasis"><em>iscl</em></span> is either absent or 0), the volume of the resonant peak increases as Q increases. For high values of Q, it is recommended that <span class="emphasis"><em>iscl</em></span> be set to a non-zero value, or that an external scaling function such as <a class="link" href="balance.html" title="balance"><em class="citetitle">balance</em></a> is used.
    </p>
        <p>
      <span class="emphasis"><em>svfilter</em></span> is based upon an algorithm in Hal Chamberlin's <span class="emphasis"><em>Musical Applications of Microprocessor</em></span>s (Hayden Books, 1985).
    </p>
      </div>
      <div class="refsect1">
        <a id="idp154487200"></a>
        <h2>Examples</h2>
        <p>
      Here is an example of the svfilter opcode. It uses the file <a class="ulink" href="examples/svfilter.csd" target="_top"><em class="citetitle">svfilter.csd</em></a>.

      </p>
        <div class="example">
          <a id="idp154488976"></a>
          <p class="title">
            <strong>Example 887. Example of the svfilter opcode.</strong>
          </p>
          <div class="example-contents">
            <p>See the sections <a class="link" href="UsingRealTime.html" title="Real-Time Audio"><em class="citetitle">Real-time Audio</em></a> and <a class="link" href="CommandFlags.html" title="Csound command line"><em class="citetitle">Command Line Flags</em></a> for more information on using command line flags.</p>
            <pre class="programlisting">
<span class="csdtag">&lt;CsoundSynthesizer&gt;</span>
<span class="csdtag">&lt;CsOptions&gt;</span>
<span class="comment">; Select audio/midi flags here according to platform</span>
<span class="comment">; Audio out   Audio in    No messages</span>
-odac           -iadc     -d     <span class="comment">;;;RT audio I/O</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o svfilter.wav -W ;;; for file output any platform</span>
<span class="csdtag">&lt;/CsOptions&gt;</span>
<span class="csdtag">&lt;CsInstruments&gt;</span>

<span class="comment">; Orchestra file for resonant filter sweep of a sawtooth-like waveform. </span>
<span class="comment">; The seperate outputs of the filter are scaled by values from the score,</span>
<span class="comment">; and are mixed together.</span>
<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">kr</span> <span class="op">=</span> 2205
<span class="ohdr">ksmps</span> <span class="op">=</span> 20
<span class="ohdr">nchnls</span> <span class="op">=</span> 1
  
<span class="oblock">instr</span> 1
  
  idur     <span class="op">=</span> p3
  ifreq    <span class="op">=</span> p4
  iamp     <span class="op">=</span> p5
  ilowamp  <span class="op">=</span> p6              <span class="comment">; determines amount of lowpass output in signal</span>
  ihighamp <span class="op">=</span> p7              <span class="comment">; determines amount of highpass output in signal</span>
  ibandamp <span class="op">=</span> p8              <span class="comment">; determines amount of bandpass output in signal</span>
  iq       <span class="op">=</span> p9              <span class="comment">; value of q</span>
  
  iharms   <span class="op">=</span>        (<span class="ohdr">sr</span><span class="op">*</span>.4) <span class="op">/</span> ifreq
  
  asig    <span class="opc">gbuzz</span> 1, ifreq, iharms, 1, .9, 1             <span class="comment">; Sawtooth-like waveform</span>
  kfreq   <span class="opc">linseg</span> 1, idur <span class="op">*</span> 0.5, 4000, idur <span class="op">*</span> 0.5, 1     <span class="comment">; Envelope to control filter cutoff</span>
  
  alow, ahigh, aband   <span class="opc">svfilter</span> asig, kfreq, iq
  
  aout1   <span class="op">=</span>         alow <span class="op">*</span> ilowamp
  aout2   <span class="op">=</span>         ahigh <span class="op">*</span> ihighamp
  aout3   <span class="op">=</span>         aband <span class="op">*</span> ibandamp
  asum    <span class="op">=</span>         aout1 <span class="op">+</span> aout2 <span class="op">+</span> aout3
  kenv    <span class="opc">linseg</span> 0, .1, iamp, idur <span class="op">-</span>.2, iamp, .1, 0     <span class="comment">; Simple amplitude envelope</span>
          <span class="opc">out</span> asum <span class="op">*</span> kenv
  
<span class="oblock">endin</span>


<span class="csdtag">&lt;/CsInstruments&gt;</span>
<span class="csdtag">&lt;CsScore&gt;</span>

<span class="stamnt">f</span>1 0 8192 9 1 1 .25
  
<span class="stamnt">i</span>1  0 5 100 1000 1 0 0  5  <span class="comment">; lowpass sweep</span>
<span class="stamnt">i</span>1  5 5 200 1000 1 0 0 30  <span class="comment">; lowpass sweep, octave higher, higher q</span>
<span class="stamnt">i</span>1 10 5 100 1000 0 1 0  5  <span class="comment">; highpass sweep</span>
<span class="stamnt">i</span>1 15 5 200 1000 0 1 0 30  <span class="comment">; highpass sweep, octave higher, higher q</span>
<span class="stamnt">i</span>1 20 5 100 1000 0 0 1  5  <span class="comment">; bandpass sweep</span>
<span class="stamnt">i</span>1 25 5 200 1000 0 0 1 30  <span class="comment">; bandpass sweep, octave higher, higher q</span>
<span class="stamnt">i</span>1 30 5 200 2000 .4 .6  0  <span class="comment">; notch sweep - notch formed by combining highpass and lowpass outputs</span>
<span class="stamnt">e</span>


<span class="csdtag">&lt;/CsScore&gt;</span>
<span class="csdtag">&lt;/CsoundSynthesizer&gt;</span>
</pre>
          </div>
        </div>
        <p><br class="example-break" />
    </p>
      </div>
      <div class="refsect1">
        <a id="idp154493296"></a>
        <h2>Credits</h2>
        <p>
      </p>
        <table border="0" summary="Simple list" class="simplelist">
          <tr>
            <td>Author: Sean Costello</td>
          </tr>
          <tr>
            <td>Seattle, Washington</td>
          </tr>
          <tr>
            <td>1999</td>
          </tr>
        </table>
        <p>
    </p>
        <p>New in Csound version 3.55</p>
      </div>
    </div>
    <div class="navfooter">
      <hr />
      <table width="100%" summary="Navigation footer">
        <tr>
          <td width="40%" align="left"><a accesskey="p" href="sumarray.html">Prev</a> </td>
          <td width="20%" align="center">
            <a accesskey="u" href="OpcodesTop.html">Up</a>
          </td>
          <td width="40%" align="right"> <a accesskey="n" href="syncgrain.html">Next</a></td>
        </tr>
        <tr>
          <td width="40%" align="left" valign="top">sumarray </td>
          <td width="20%" align="center">
            <a accesskey="h" href="index.html">Home</a>
          </td>
          <td width="40%" align="right" valign="top"> syncgrain</td>
        </tr>
      </table>
    </div>
  </body>
</html>
